Breast cancer is the most common cancer in women and the second most deadly cancer. The prevalence of breast cancer in 2001 was 90-100 per 100,000 people in the United States and 50-70 per 100,000 people in Europe. The onset of this disease is increasing worldwide. Risk factors for breast cancer include race, age, mutations in the cancer suppressor genes BRCA-1, BRCA-2, and p53. Alcohol consumption, high fat diets, lack of exercise, exogenous postmenopausal hormone and ionizing radiation also increase the risk of breast cancer. The prognosis of breast cancer is worse in estrogen receptors and progesterone receptor negative breast cancers (ER- and PR-, respectively), large tumor size, result of a high grade cytologic diagnosis, and people under 35 years of age (Goldhirsch et al. J. Clin. Oncol. 19: 3817-27). Approximately 212,000 new invasive breast cancer cases and 58,000 new noninvasive breast cancer cases were estimated to be diagnosed in 2005 and 40,000 women were expected to die of breast cancer in 2005.
After surgery, current methods of treating breast cancer require additional adjuvant treatment to reduce future recurrence, such chemotherapy, antihormonal therapy, target therapy or radiotherapy. Of these, chemotherapy is one of the anti-cancer therapies. The pathological status of a breast cancer patient varies from patient to patient depending on the condition of the cancer, the size of the tumor, the pathologic stage of the tumor, or other factors. Thus, since different pathological conditions and different responses in a breast cancer patient, some patients may benefit from chemotherapy with anticancer drugs, but others may not. Continuous administration of chemotherapy to patients who are not as effective as chemotherapy may increase the side effects and cause unwanted pain to the patient.
In this regard, prior to the administration of an anti-cancer drug to a breast cancer patient, methods are needed to accurately predict the effectiveness of chemotherapy in those patients.